VARIOS FORMATOS EN UNA SOLA CELDA

Early theories of the AB were so motivated to find the cause of the detriment in T2 identification that they failed to address the issue of how targets were selected in a RSVP. Olivers and Watson (2006) criticise this, specifying that top-down control over the selection process may be a key factor in understanding the blink. By carefully manipulating the featural similarity between T1 and T2 in a RSVP they were able to

show the importance of top-down processing in the AB. Participants were asked to search through a stream of distracter letters for a specifically coloured letter (T1) and a dot pattern (T2) and report the letter and the number of dots they saw. T2 was either the same colour as T1, the same colour as the distracters, or a unique colour. Findings showed that the AB was much larger when T2 was the same colour as the distracters compared to when it was the same colour as T1. This suggests that the presumed role of the attentional set is correct and attention is programmed to select targets and actively inhibit distracters.

Crucial to the current work is the fact that other researchers have used the RSVP methodology to show the influence of top-down processing in the control of attention. The findings of Olivers and Watson (2006) provide evidence for contingent capture (Folk et al., 1992); items matching the target-defining features will be

selected; items which do not match will be inhibited. They utilize the contingent capture hypothesis to further understand the workings of the AB; however others have utilised the AB paradigm to gain further evidence for contingent capture. For

example, Folk, Leber and Egeth (2002) presented participants with a RSVP containing one target and one peripheral distracter. The distracter was presented before the target and it was either congruent or incongruent with the attentional set. When the distracter was incongruent it did not capture attention and did not cause an AB on the target, however when it was congruent with the set it did cause an AB. Folk et al. (2002) associated the deficit with spatially shifting attention to the

distracter (it was shown peripheral to the RSVP), yet Ghorashi, Zuvic, Visser, and Di Lollo (2003) questioned whether it was partly due to the processing of this distracter. They conducted a similar study but presented all items to the same spatial location. Again there was an AB when a distracter shared target-defining features with the

subsequent target. The deficit found lasted up to 600ms SOA, therefore the temporal deficit due to contingent capture very closely follows the pattern of performance found in a dual target RSVP when T1 must be processed. This not only shows that the task-irrelevant distracter was being processed to some extent, it also shows

similarities between the different findings of the AB and contingent capture, revealing how useful the RSVP methodology can be.

In conjunction with the recent interest into the top-down influence over attentional capture (outlined in Chapter One), current theories of the AB are now suggesting a larger impact of top-down control than was previously projected. One prominent model at the present time is the Temporary Loss of Control model (TLC; Di Lollo, Kawahara, Ghorashi, & Enns, 2005). Di Lollo and colleagues propose that instead of the AB resulting from resource depletion, or a limited capacity processing system, it occurs at an ‘executive level’ and arises because when T1 is being

processed the system temporarily loses top-down control. The attentional set used to complete the RSVP configures the processing system as an input filter which allows items matching the target-defining features to pass through, but denies entry to distracters. This top-down filter requires constant feedback but when the central processor is engaged in processing T1 it can no longer continue to send feedback. The absence of any signals means that the filter may come under exogenous control. Di Lollo, Kawahara, Ghorashi, & Enns specify that the characteristics of the targets and distracters have a critical role at this point. If the T1+1 item matches the attentional control settings it will activate the original set and pass through the filter for further processing, resulting in lag-1 sparing. If the item does not match the original set it will trigger an exogenous set, causing an AB on the items at lags 2+ (even if these items match the original top-down set) until feedback can again be sent to the endogenous

set and the top-down system can regain control. The theory therefore proposes that the AB is not due to the number of items to be processed, but the fact that the processing system can only assume one configuration at a time. The processing of T1 only takes 100ms (Raymond et al., 1992) but Di Lollo, Kawahara, Ghorashi, & Enns (2005) suggest that the lengthy deficit caused by this processing is due to the costs associated with switching set.

The TLC model can account for more recent findings of the AB than previous models. For example, Olivers, van der Stigchel, and Hulleman (2007) presented participants with a RSVP containing three targets displayed successively, therefore T2 appeared at lag 1 and T3 appeared at lag 2. According to earlier models an AB effect should be found with lag-1 sparing (T2 would be easily identifiable) followed by a deficit in performance at later lags (T3 would be difficult to identify). What they actually found was that performance was high for all three targets and there was no evidence of an AB. The TLC model posits that this finding occurs because the system does not lose control over the input as the item at lag 1 matches the attentional set and so does not trigger an exogenous set.